Foamed metals have high strength-to-weight ratios and are extremely useful as load-bearing materials and as thermal insulators. Metallic foams are characterized by high impact energy absorption capacity, low thermal conductivity, good electrical conductivity and high absorptive acoustic properties.
Foamed metals have been described previously, e.g. in U.S. Pat. Nos. 2,895,819, 3,300,296 and 3,297,431. In general such foams are produced by adding a gas-evolving compound to a molten metal. The gas evolves to expand and foam the molten metal. After foaming, the resulting body is cooled to solidify the foamed mass thereby forming a foamed metal solid. The gas-forming compound can be metal hydride, such as titanium hydride, zirconium hydride, lithium hydride, etc. as described in U.S. Pat. No. 2,983,597.
A recent development in the production of lightweight foamed metal is described by Jin in U.S. Pat. No. 4,973,358 issued Nov. 27, 1990. In that patent, a precursor composite of a metal matrix and finely divided solid stabilizer particles was heated above the liquidus temperature of the metal matrix and gas bubbles were discharged into the molten metal composite below the surface to thereby form a foamed melt on the surface of the molten metal composite. When this foam was cooled, it formed a solid foamed metal having a plurality of closed cells and the stabilizer particles dispersed within the metal matrix.
The metal matrix precursor composite used in the process of U.S. Pat. No. 4,973,358 was one in which the contained stabilized particles were quite uniform in size and were fully wetted by the matrix material. One such product that was used was the aluminum matrix composite sold under the trademark DURALCAN by Alcan Aluminum Corporation. However, such composites are expensive to produce and result in a relatively expensive foam product.
Metal foam generated from such precursor materials have as stabilizing particles monolithic or blocky particles, typically SiC or alumina. These precursor composites are also produced under reduced pressures or even under vacuum conditions. Foam generated from such material has been found to be difficult to cut except for the lowest density material.
An object of this invention is to provide metal foams having desirable properties using a relatively inexpensive procedure.
A further object of this invention is to provide an alternative to standard metal matrix precursor composites used for producing metal foams.
Another further object is to provide a relatively inexpensive precursor for the production of foamed metals.
A further object is to provide a stabilized metal foam which is easier to machine than previous stabilized foam materials.
A still further object is to provide a stabilized metal foam with modified and adjustable crush properties.